Annales Societatis Geologorum Poloniae (2009), vol. 79: 365–374.
DETECTION OF NEAR-SURFACE GEOLOGICAL HETEROGENEITY
AT STARUNIA PALAEONTOLOGICAL SITE AND VICINITY
(CARPATHIAN REGION, UKRAINE)
BASED ON MICROGRAVITY SURVEY
S³awomir PORZUCEK & Janusz MADEJ
Fac ulty of Ge ol ogy, Geo phys ics and En vi ron men tal Pro tec tion, AGH Uni ver sity of Sci ence and Tech nol ogy, Al. Mick iewicza 30, 30- 059 Kraków, Po land, e- mail: porzucek@agh.edu.pl, madej@geol.agh.edu.pl Porzucek, S. & Madej, J., 2009. De tec tion of near- surface geo logi cal het ero ge ne ity at Sta runia pa lae on to logi cal site and vi cin ity (Car pa thian re gion, Ukraine) based on mi cro grav ity sur vey. An nales So cie ta tis Ge olo go rum Po lo niae, 79: 365–374.
Ab stract: Re sults of a mi cro grav ity sur vey per formed in the aban doned Sta runia ozo ke rite mine (Car pa thian
re gion, Ukraine), where in the early 20th cen tury well pre served re mains of large, ex tinct mam mals were found, are dis cussed in the pa per. A number of grav ity anoma lies in di cat ing the geo logi cal het ero ge ne ity at the sub- Quaternary strata have been ob served. The as sumed meas ure ment ob ser va tions also en abled the authors to in ter pret the re sults in view of den sity changes in the Qua ter nary strata. Most of the reg is tered mi cro anoma lies co in cide with the high- halite and ozo keritic Mio cene salt- bearing Vo ro tyshcha beds. The dis tri bu tion of the mi cro anoma lies re veals nei ther their cor re la tion with the thick ness of over bur dens, nor any grav ity im pact of nu mer ous aban doned wells. Grav ity anoma lies were mostly con nected with the li thol ogy of sedi ments and rocks ob tained from geo logi cal bore holes drilled in the years 2007 and 2008, on the ba sis of which the anoma lies’ ori gin could be de ter mined. A con cen tric, rela tively nega tive grav ity mi cro anom aly of ca. 25 m in di ame ter was reg is tered in the place, where very well pre served rel ics of the woolly rhi noc eros had been found. They may be in dica tive of the ex is tence of Pleis to cene lakes (and/or pa laeos wamps), into which the woolly rhi noc er oses had sunk. Hence, an as sump tion can be made that the fur ther search for suc ces sive zoo logi cal rel ics can be made in ar eas with simi lar anoma lies un der the low- density sub- Quaternary sub crop.
Key words: geo phys ics, mi cro grav ity, Qua ter nary sedi ments, Sta runia, Car pa thian re gion, Ukraine.
Manu script re ceived 18 May 2009, ac cepted 20 October 2009
IN TRO DUC TION
Mi cro grav ity sur vey was a part of an in ter dis ci pli nary re search proj ect fo cused on study of the Sta runia area. Dur -ing the 2006–2009 pe riod, com pre hen sive in ves ti ga tions were car ried out in an aban doned ozo ke rite (earth wax) mine at Sta runia (Ko tarba, 2009), about 130 kilo me tres south east of Lviv, Ukraine (Fig. 1), where re mains of a mam moth and three woolly rhi noc er oses, and one nearly com pletely pre served rhi noc eros were found in 1907 and 1929. Such a good state of pres er va tion can be at trib uted to the pres ence of pre serv ing com po nents, i.e. oil and brines (Ko tarba et al., 2009). These me dia abun dantly oc cur in the near- surface beds of the Sta runia area.
Com plex sur veys aim ing at a de tailed rec og ni tion of the geo logi cal set ting in this area started in 2004 (Ko tarba, ed., 2005). Gra vime try was one of the meas ure ment meth ods and its use was dic tated by the vari able den sity of rocks, caused be the pres ence of brines, oil and ozo ke rite veins.
In the course of grav ity sur veys high halite and ozo ke -rite beds were lo cal ized within the Mio cene salt- bearing Vo ro tyshcha beds (Madej & Porzucek, 2005), through which oil mi grated from the deeper for ma tions to the sur -face (Kol tun et al., 2005). Grav ity sur veys were con tin ued in the years 2007 to 2008 and as a re sult a de tailed de scrip -tion of geo logi cal set ting in the area of former ozo ke rite mine could be worked out (Porzucek & Madej, 2009). At that time, mi cro grav ity sur veys aim ing at rec og niz ing geo -logi cal set ting of the Qua ter nary se quence were also made. They were fo cused on de ter min ing ar eas where ex tinct ani -mal re mains can be po ten tially found.
METHOD
The grav ity meth ods (mi cro grav ity sur veys be ing their vari ant) make use of the grav ity field dis tri bu tion as a func tion of depth varia tion of the ana lysed rock for ma tion (Fajk
le wicz, 2007). Such a varia tion can be at trib uted to the pres -ence of geo logi cal forms and struc tures, the bulk den sity of which var ies from those of the sur round ing rocks.
The re sults of grav ity sur veys are pre sented in the form of grav ity anoma lies. If the den sity of rocks mak ing up the geo logi cal struc ture is lower than that of the sur round ings,
Fig. 1. Sketch map of the Starunia palaeontological site and sur round ing area (Carpathian re gion, Ukraine) show ing the lo ca tion of the microgravity sur vey
then a rela tively nega tive grav ity anom aly is gen er ated. A rela tively posi tive anom aly is re spon si ble for the pres ence of a struc ture of in creased bulk den sity com pared to the sur -round ing rocks. The mag ni tude of the ob served anom aly de pends on the dif fer ence in bulk den sity be tween geo logi -cal struc tures, their depth and size.
The meas ured dis tri bu tion of grav ity anoma lies is in ter -preted and on this ba sis their re la tion with the geo logi cal set ting can be es tab lished.
In the ana lysed case this re la tion was lim ited to the analy sis of anoma lies, which can be at trib uted to the het ero -ge nei ties in the near- surface bed of the rock for ma tion. At that depth in ter val, mor pho logi cal fos sil forms can oc cur, such as old swamps, marshes and lakes, be ing po ten tial traps for ani mals. It was as sumed that such forms have their rep re sen ta tion in the form of rela tively nega tive grav ity anoma lies.
Bear ing in mind the ob jec tive of sur veys, i.e. the rec og -ni tion of near- surface beds of the rock for ma tion, the authors lo cal ized the grav ity sta tions at a dis tance of 10 m to 12.5 m. Mi cro grav ity ob ser va tions were car ried out with a Ca na dian gra vime ter CG-3 Scin trex (ac cu racy ±0.01 mGal, and re peat abil ity ±0.005 mGal).
The re sults of ob ser va tions cre ated the ba sis for cal cu lat ing grav ity mi cro anoma lies at the grav ity sta tions. Al low -ances for the force of grav ity were made in the cal cu la tions. The de ter mined Bou guer mi cro anoma lies were re lated to the lo cal ref er ence level.
STUDY AREA
Microgravity sur veys were made in the years 2007 to 2008 over a to tal area of ca. 0.2 km2. The study area is pre sented in Fig. 1 at the back ground of a sim pli fied top o -graphic out line. In 2007, the sur veys cov ered an area of ca. 0.1 km2 in a grid of mesh 12.5×12.5 m, and in 2008 in a sim i lar area, in a grid of 10×10 m mesh. In 2007, af ter prior anal y sis of the re sults, more de tailed microgravity sur veys were per formed in two ar eas I and II, shown in Fig. 1. The mea sure ments were made in the ac ces si ble nodes of a square grid (6.25 m side) in both these places, cov er ing the ar eas of 130×110 m and 70x50 m.
GEO LOG I CAL SET TING
In the area of the aban doned Sta runia ozo ke rite mine, the Qua ter nary sedi ments of the Ve lyky Lu kavets River val -ley are de vel oped as clayey muds with plant re mains, peat, bio genic muds, and peat muds (Soko³owski et al., 2009; Soko³owski & Stachowicz Rybka, 2009). De tails of ge ol -ogy and pe tro leum oc cur rence in the Sta runia area were pub lished by Ada menko et al. (2005), Al ex androwicz (2004, 2005), Kol tun et al. (2005), Ko rin (2005), Ko tarba & Stachowicz- Rybka (2008), Soko³owski et al. (2009), Soko-³owski & Stachowicz- Rybka (2009) and Stachowicz- Rybka
et al. (2009) (see also ref er ences therein).
The top sur face of the salt- bearing Mio cene Vo ro -tyshcha beds of the Boryslav- Pokuttya Unit in the Sta runia
area, which un der lie Qua ter nary de pos its, oc curs at a maxi -mum depth of 17 me tres (Soko³owski et al., 2009). The Mio cene strata are sandstone- claystone brec cias with hal ite, potassium salt, gyp sum and cal cite lay ers, and veins of ozo -ke rite (Mi tura, 1944; Ko rin, 2005). Within these sedi ments many brine and salt wa ter springs oc cur in the Sta runia’s vi -cin ity. The Boryslav- Pokuttya Unit is the main oil and gas res er voir in the Ukrain ian Car pa thi ans. Tec toni cally, the unit rep re sents a stack of su per im posed nap pes, each of them com pris ing the flysch se quence cov ered by mo lasse (Kol tun et al., 2005).
RE SULTS
Microgravity sur veys en abled au thors to ob tain a dis tri bu tion of Bouguer grav ity anom a lies (cf. Fig. 2). An ex ten -sive, rel a tively neg a tive grav ity anom aly dom i nates there. Its NW to SE trend cor re sponds with the Mio cene Vorotyshcha saltbear ing beds (Korin, 2005). The mod el ling re -veals that the pres ence of a high-ha lite sa line for ma tion with ozokerite veins, de scribed by Mitura (1944), is a source of this microanomaly (Porzucek & Madej, 2009). The den sity in this part of the for ma tion is over 0.2 g×cm–3, i.e. lower than the den sity of the sur round ing rocks.
The domi nant anom aly con sists of nega tive grav ity anoma lies, which ow ing to their am pli tude and range will be later called mi cro anoma lies (Fajk le wicz, 1980). These mi cro anoma lies are in dica tive of den sity varia tions of the near- surface part of the for ma tion.
Six anoma lous ar eas from A to F (Fig. 2) can be dis tin -guished from the analy sis of dis tri bu tion of Bou guer anoma lies. Nega tive, con cen tric, loop- shape anoma lies are visi ble in anoma lous ar eas B, C, D and E. They de note the ex is tence of lower density beds in these places. The analy -sis of litho logi cal logs of bore holes ex plic itly shows that these mi cro anoma lies do not have any cor re spon dence with the in creased thick ness of the over bur den.
In the north- western part of the ana lysed area, near the Rinne fault, an anoma lous area A was de ter mined. In the grav ity anom aly dis tri bu tion, this area can be seen as a lo cal low er ing of grav ity hori zon tal gra di ent, in dica tive of the ex is tence of lower density beds. Litho logi cal bore hole logs re -veal that their for ma tion may be at trib uted to the ex is tence of a sev eral metre- thick peat layer, the den sity of which is much lower than that of the re main ing ones (Soko³owski et
al., 2009).
Simi lar to anom aly A, an other grav ity anom aly area de noted as F, is shown as a low er ing of grav ity hori zon tal gra -di ent. It can be found near the con flu ence of the Rinne Stream to the Ve lyky Lu kavets River. The cause of its gen -era tion re mains un known. Judg ing from bore hole No. 3’ on the river bank, the anom aly can not be at trib uted to the ex is -tence of the peat layer.
Anoma lous ar eas A and B were sub jected to more de -tailed mi cro gra vimet ric sur veys, the re sults of which will be pre sented later in this pa per. It should be noted that the woolly rhi noc eros was found at the edge of the mi cro anom -aly in area B, whereas area A was close to mud vol ca noes.
IN TER PRE TA TION AND DIS CUS SION
The in ter pre ta tion of grav ity re sults lies in find ing a re la tion be tween the meas ured dis tri bu tion of grav ity mi cro anoma lies and the geo logi cal set ting. How ever, the meas ured dis tri bu tion of grav ity mi cro anoma lies is a su per po si tion of grav ity im pact of re gional struc tures and lo cal geo -logi cal forms. The in flu ence of lo cal forms is rep re sented by lo cal mi cro anoma lies, whereas deep and large geo logi cal struc tures are caused by re gional anoma lies.The quali ta tive in ter pre ta tion lies in speci fy ing, which of the meas ured grav ity anom aly area is re gional and which one is lo cal. This can be done with vari ous meth ods, and the se lec tion of the proper one de pends on a number of fac tors. The most im por tant ele ment de ter min ing its se lec tion is the
form of the re gional area ob tained from trans for ma tion, which should ap proxi mate the shape of the meas ured anoma lies. In prac tice, the re gional area is as sumed to rep re -sent a dis tri bu tion hav ing a smooth shape of iso lines. At the same time, the in ter preted shape of the re gional area should con vene with the re gional geo logi cal set ting. There fore, the de ter mined trend of re gional area should be first of all as -cribed a geo logi cal in ter pre ta tion in the dis cussed case. The trend will cor re spond to the grav ity in flu ence of the bearing struc ture. For de ter min ing the trend, i.e. the shape of the re gional area, the Griffin’s av er ag ing method was used (Grif fin, 1949). The choice of this method was dic tated by its filter based char ac ter. The shape of the thus cal cu lated field in the area of mi cro gra vimet ric meas ure ments re mains un af fected by other, dis tant fields of grav ity dis tur
bances. In the Griffin’s method, the weighted av er age of a cir cle drawn from the meas ure ment sta tion point is as sumed to be the re gional grav ity anom aly at that point. The shape of the thus de fined re gional anom aly de pends on the as -sumed ra dius of av er ag ing of the meas ured field val ues. Thus, a number of lo cal anoma lies can be ob tained when calculating the lo cal anom aly as a dif fer ence be tween the meas ured value and the re gional anom aly. In re al ity, how -ever, only one lo cal anom aly ex ists as its ex is tence de pends on a spe cific near- surface geo logi cal set ting. Ac cord ingly, cal cu lated anoma lies are usu ally called lo cal re sid ual ano-malies, which, ow ing to their small size and am pli tude, will be later called re sid ual mi cro anoma lies. Re sid ual mi cro -anoma lies were de ter mined with the Griffin’s method for two ra dii: 50 m and 25 m long.
The dis tri bu tions of re sid ual microanomalies cal cu lated on the ba sis of val ues of a re gional area, es tab lished with the Grif fin’s method for ra dii equal to 50 m and 25 m, are pre -sented in Figs 3 and 4, re spec tively.
The dis tri bu tion of re sid ual microanomalies for a ra dius equal to 50 m is given in Fig. 3. The courses of rel a tively pos i tive and neg a tive lo cal microanomalies can be seen in the dis tri bu tions. They con tain the al ready de ter mined anom a lous ar eas (A to E). The cal cu la tion of re sid ual anom -a lies with the Grif fin’s method re sults in los ing in for m-a tion at the edges of the ana lysed area, the width of which equals to the as sumed ra dius, and the anom a lous area F is not in di -cated. The ob tained courses of microanomalies rep re sent the dis tri bu tion of den sity in the sub-Quaternary part of the Miocene beds.
NEAR-SUR FACE GEO LOG I CAL HET ER O GE NE ITY AT STARUNIA
369
The dis tri bu tion of re sid ual microanomalies ob tained for a ra dius equal to 25 m gen er ally rep re sents the dis tri bu tion of den sity in Qua ter nary strata (Fig. 4). The al ready de ter mined anom a lous ar eas are clearly vis i ble in the dis tri bu -tion, except for area F.
A rel a tively neg a tive re sid ual anom aly of con cen tric shape ap pears in the anom a lous area A (Fig. 4). De scrip tions will be used for de not ing all the microanomalies fur -ther in this pa per. As al ready men tioned, the causes of its gen er a tion should be at trib uted to the pres ence of a peat layer. This is ev i denced by lithological logs of bore holes Nos 13 and 14, lo cated at the edges of the microanomaly, where a 3-m-thick peat layer was found. De tailed microgravity sur veys were made in this area. The re sults are pre -sented in Fig. 5 in the form of a dis tri bu tion of Bouguer
microanomalies and a dis tri bu tion of re sid ual microano-malies cal cu lated with the Grif fin’s method for ra dii equal to 10, 15, 20 and 25 m, re spec tively. A microanomaly can be ob served even for a 10 m ra dius. This may in di cate a very shal low or i gin of the microanomaly and prove its re la tions with the peat layer. The suc ces sive dis tri bu tions of re sid ual microanomalies reach deeper lay ers, data are gath -ered from the sur face, and the range of peat occurrence can be better determined.
The al ready de fined anom a lous area B (Fig. 2) is very in ter est ing as zoo log i cal rel ics, e.g. a very well pre served woolly rhi noc eros, were found there. In the dis tri bu tion of re sid ual anom a lies (Fig. 4), two rel a tively neg a tive re sid ual microanomalies B1 and B2 can be found in that area. Mi cro-
anom aly B1 con tin ues to the north and north west, as sum ing
a V shape. Data from bore holes Nos 21 and 22 point to the ex is tence of over 1mthick peat layer, very near the sur face. There fore, microanomaly B can be re lated with the ex -is tence of these lay ers, anal o gous to microanomaly A. Microanomaly B2 con tin ues to the west from the place of
find ing of zoo log i cal rel ics. Bore hole data are not in dic a tive of the ex is tence of lower-density beds, generating this anomaly.
De tailed microgravity sur veys were per formed in the anom a lous area B and the re sults are pre sented in Fig. 6. In the Bouguer microanomaly dis tri bu tion (Fig. 6A), a frag
-ment of microanomaly B1 is well vis i ble and the rel a tively
neg a tive microanomaly B2 splits into two microanomalies
B2a and B2b. Sim i lar to de tailed sur veys of anom a lous area
A, the re sid ual microanomaly was de ter mined with the Grif -fin’s method for ra dii equal to 10, 15, 20 and 25 m (Fig. 6B–E). The dis tri bu tions for the suc ces sively in creas ing ra -dii il lus trate deeper sources of microanomaly gen er a tion. These dis tri bu tions con firm that near-sur face den sity changes are the source of microanomaly B1, there fore, link
-ing this microanomaly with the ex is tence of peat is jus ti fied. Bore holes Nos 30, 30N and 33 were drilled within the area
NEAR-SUR FACE GEO LOG I CAL HET ER O GE NE ITY AT STARUNIA
371
Fig. 5. Sur face dis tri bu tion of the Bouguer microanomalies (A) and sur face dis tri bu tions of the re sid ual microanomalies (B–E) (re -gional field was cal cu lated us ing the Grif fin’s method for ra dii: 12.5, 15, 20 and 25 m, re spec tively) in area I
of microanomaly B2b. The lithological logs of these bore
-holes do not point to the ex is tence of lower-den sity beds,
i.e. po ten tial sources of the microanomaly. It seems likely
that the microanomaly was gen er ated from mi nor den sity changes within the Qua ter nary strata, which do not have any di rect con nec tion with the li thol ogy, and which can be inferred from the nonconcentric shape of the mi croanom a -lies.
The rel a tively neg a tive microanomaly B2b is prac ti cally
in vis i ble for a ra dius 10 m long, weakly vis i ble for a ra dius of 15 m, and clearly vis i ble for lon ger ra dii. The mi
croanom aly, ca. 25 m in di am e ter, is con cen tric in shape. Bore -holes Nos 27, 27’, 41 and 44 are lo cal ized within this mi cro- anom aly. In all these microanomalies, the over bur den dom i -nated in the lithological pro file. Nev er the less, the ex is tence of an in creased over bur den thick ness should not be as so ci -ated with the pres ence of microanomalies, which can be proved by lithological logs of bore holes Nos 40 and 43, sit -u ated be yond the range of the microanomaly. It is es pe cially well vis i ble for bore hole No. 43, which is lo cal ized within the rel a tively pos i tive microanomaly (Fig. 6B–E). Al though the bore hole data are most re li able, one should re mem ber
Fig. 6. Sur face dis tri bu tion of the Bouguer microanomalies (A) and sur face dis tri bu tions of the re sid ual microanomalies (B–E) (re -gional field was cal cu lated us ing the Grif fin’s method for ra dii: 12.5, 15, 20 and 25 m re spec tively) in area II
that these are point data. The con cen tric microanomaly B2b
points to the ex is tence of beds hav ing lower den sity than that of the sur round ing for ma tion. The shape of the mi croanom aly can be at trib uted to the grav ity im pact of the pos si -ble palaeoswamp, on the edge of which zoo log i cal rel ics were bur ied. This hy poth e sis seems to be plau si ble, es pe -cially since a woolly rhi noc eros was found at the edge of microanomaly B2b.
A con cen tric and rel a tively neg a tive re sid ual mi croanom aly is vis i ble in the croanom a lous area C (Fig. 4). Un for -tu nately, no bore holes were drilled there. This microano-maly is lo cal ized in a course of rel a tively neg a tive re sid ual microanomalies, co in cid ing with a small wa ter course run -ning from “Nadzieja 1” well to the vi cin ity of bore hole “Juliusz 2”. One can as so ci ate the course of anom a lies with the wa ter route, and with the low den sity near-sur face lay ers formed and trans formed by wa ter. Be sides, the cen tre of microanomaly C co in cides with the remains of an artificial water reservoir.
The dis tri bu tion of re sid ual microanomalies (Fig. 4) in the anom a lous area D dif fers from the dis tri bu tion of Bou-guer anom a lies (Fig. 2). Af ter re mov ing the re gional trend, a T-shape microanomaly could be dis tin guished. Bore hole No. 4N was drilled in side, whereas bore holes Nos 5N, 6N and 7 are lo cated at the edge of this microanomaly. A frag -ment of the microanomaly, form ing the up per part of the “T”, can be ex plained by the ex is tence of swamp ar eas, which an a log i cally to microanomaly C, can gen er ate a rel a tively neg a tive microanomaly. The cause of or i gin of the re -main ing part of the microanomaly (greater am pli tude and vis i ble in the dis tri bu tion of the Bouguer anom aly; Fig. 2) is prob a bly dif fer ent. The Eu ler deconvolution method (Thompson, 1982) in a ver sion ad justed to in ter pre ta tion of microgravity re sults (Porzucek, 2004) was used for de ter -min ing the depth of the body re spon si ble for gen er at ing this part of the microanomaly. Ac count ing for the elon gated shape of the microanomaly, the au thors as sumed that the microanomaly was gen er ated by a hor i zon tal cyl in der. The cal cu la tions in di cated that the axis of the as sumed hor i zon tal cyl in der was lo cated at a depth of ca. 8.5 m. Un for tu -nately, bore holes Nos 5N, 6N and 7 were lo cated at the edges of the microanomaly and the lithological sec tion of beds in the cen tral parts of the microanomaly re mained un -known. How ever, the high sand and gravel con tents were ob served for these bore holes. Per haps, more such beds are pres ent within the microanomaly, and their density is lower than that of the clayey muds that dominate in the Quaternary strata.
The anom a lous area E (Fig. 2), is an other rel a tively neg a tive re sid ual grav ity microanomaly (Fig. 6). The course of these microanomalies clearly co in cides with the course of the Velyky Lukavets River. Hence, a con clu sion ap pears that the river pri mar ily con trib uted to the rel a tively neg a tive microanomaly for ma tion. The vi cin ity of the river, which is cut into the for ma tion by sev eral metres, re sults in dewatering and weak en ing of the for ma tion in its im me di ate neigh bour hood. More over, the lo cal iza tion of mea sure ment sta -tions in the im me di ate vi cin ity of the river in tro duces the element of er ror, be cause of the gravity impact of the com -plex morphology of the area.
CON CLU SIONS
Microgravity sur veys in the area of aban doned Starunia ozokerite mine re vealed six anom a lous ar eas of rel a tively low grav ity val ues (Fig. 2). Four of them (B, C, D and E) are lo cal ized un der a layer, the den sity of which is lower com -pared to the neigh bour hood, and be long ing to the Mio cene Vorotyshcha salt-bear ing beds (Porzucek & Madej, 2009). The anom a lous area A is lo cated in the Rinne fault zone (Porzucek & Madej, 2009), whereas area F at the con flu -ence of the Rinne Stream with the Velyky Lukavets River.
The re sid ual grav ity microanomalies de ter mined on the ba sis of the Grif fin’s method were cal cu lated dur ing in ter -pre ta tion. The dis tri bu tion of re sid ual grav ity microano-malies cal cu lated for a ra dius of 50 m showed a den sity vari abil ity of the sub-Qua ter nary part of the Mio cene beds (Fig. 3). By re mov ing the re gional trend from the Bouguer anom aly by em ploy ing the Grif fin’s method for a ra dius equal to 25 m, the au thors ob tained a dis tri bu tion of re sid ual grav ity anom a lies, be ing a rep re sen ta tion of the dis tri bu tion of den sity in the Qua ter nary strata (Fig. 4). This dis tri bu tion con firmed the ex is tence of ear lier anom a lous ar eas, mak ing their de scrip tion more pre cise. Ac cord ingly, the rel a tively neg a tive microanomalies A and B1 (Fig. 4) should be as so
-ci ated with the ex is tence of a shal low peat layer. This has been also proved by detailed investigations in areas A and B (Figs 5, 6).
The courses of rel a tively neg a tive re sid ual grav ity microanomalies are vis i ble in Fig. 4; af ter re lat ing them with ar eas C and D one may ar rive at a con clu sion that their or i gin is con nected with the ex is tence of near-sur face loose lay ers formed by the ac tiv ity of small water courses.
The ma jor part of microanomaly D (Fig. 4) may be at -trib uted to the po ten tial ex is tence of high sand and gravel lay ers in the Qua ter nary strata.
Area E is cer tainly re lated with the ex is tence of the Velyky Lukavets River, which may cause a de crease in the den sity of the neigh bour ing beds by dewatering pro cesses. The grav ity val ues may be also low ered ow ing to the com -plex landscape.
De tailed microgravity sur veys en abled find ing mi cro-anom aly B2b (Fig. 6). At its edge, a very well pre served
woolly rhi noc eros was pre vi ously found. Should the hypo-the sis that hypo-the rhi noc eros had sunk in hypo-the palaeoswamp be true, the area of the grav ity microanomaly might co in cide with the range of the swamp.
Microgravity sur veys were per formed in the area of the aban doned Starunia ozokerite mine with nu mer ous shafts open ing up into the field. Based on our ex pe ri ence, aban doned shafts were ob served to have no im pact on the dis tri -bu tion of grav ity microanomalies based on microgravity sur veys. De tailed sur veys per formed for the two ar eas did not re veal any in flu ence of the aban doned shafts on the mea sured grav ity val ues. This may in di cate that the av er age den sity of ma te rial, with which the shafts were cov ered, was equal or sim i lar to that of the neigh bour ing for ma tion. No de pend ence be tween the thick ness of over bur den and the dis tri bu tion of grav ity microanomalies was ob served. This con firms that the den sity of the over bur den ma te rial was similar to the density of the Quaternary strata.
Beds of the same lithological com po si tion may have dif fer ent den si ties, which in turn may gen er ate smallam pli -tude microanomalies. These anom a lies, how ever, should be big ger in size and more con cen tric in shape, like, e.g. microanomaly B2a.
The re sults of microgravity sur veys ex plic itly re veal that the most in ter est ing zones within the Pleis to cene sed i -ments should be lim ited to the sub-Qua ter nary low-den sity saltbear ing subcrop (Porzucek & Madej, 2009). The thick -ness of Qua ter nary sed i ments was in creased ow ing to flood in ci dents and pres ence of lo cal swamp ar eas (peat). Mi cro-grav ity sur veys re vealed a num ber of grav ity microano-malies in this re gion. They re flect the pres ence of changes of geo log i cal ma te rial from that of the neigh bour ing for ma -tion. De tailed anal y sis of the se lected ar eas may re sult in find ing small, con cen tric microanomalies, po ten tially con -nected with the ex is tence of hy po thet i cal palaeoswamps, where the Pleistocene animals could have drowned.
Ac knowl edge ments
Fi nan cial sup port from the Min is try of Sci ence and Higher Ed u ca tion (grant No. 139/UKR/2006/01) is kindly ac knowl edged. Re view com ments and sug ges tions by Zbigniew Fajklewicz and Zenon Pilecki were very help ful. We would like to ex press our grat i tude to John Curtis of the Col o rado School of Mines in Golden for his crit i cal com ments, which im proved this pa per.
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